Membrane switches are widely used as a special type of keyboard for calculators, computers, input devices for manipulating equipment and machinery, and for educational purposes. In U.S. Pat. No. 4,360,716 granted Nov. 23, 1982, such a switch is shown in conjunction with a learning aid wherein a template having symbols thereon is laid over the switch so that an operator, when touching such symbols, will activate such switch. This patent includes a teaching of providing conductive traces on the inner surfaces of plastic sheets held apart by screened or coated insulating dots or points on spaced centers; the combination providing what is called a broad area actuated switch. This means that relatively broad areas of switch action are defined by the conductive traces rather than specific points.
In U.S. Pat. No. 4,391,845 issued July 5, 1983, there is a membrane switch disclosed which is a point-type switch, meaning that the switch contains a number of discrete switch points, each of which is typically associated with a symbol such as one through ten or zero or a letter, or some other such instructive symbol. The 4,391,845 patent teaches the use of spacer areas which are separated from the contact paths, or traces of the switch, and which, in this patent, may be made of insulating materials screened or coated to be isolated from conductive traces. These isolated traces are taught as being built up of layers which may be either conductive ink as a first layer or have additional layers of nonconductive ink and/or an adhesive material.
These patents form a background for the present invention which has as its object the provision of a membrane switch having only two plastic layers and screen printed conductive traces with screen printed insulating spacers in conjunction with a coating carrying symbols and instructions arranged to be sufficiently thin and responsive to touch as to be actuated through multiple pages laid over the top of the switch in the manner of a book. It is a further object of the invention to provide a low-cost and sensitive membrane switch for use in conjunction with instructive aids which minimizes the use of insulating sheets of which the switch contains only two, and therefore the associated labor required by the object of the invention to provide a membrane switch which can be fabricated by a variety of processing steps, including printing, screening, lithography for both appearance and symbol purposes, and for conductive and insulating traces and moreover, wherein the various coatings are protected against wear, moisture and damage by being within the envelope of the membrane switch.